Conventionally, in a case in which a hub shell is provided with a freewheel, an axially outwardly extending tubular support is provided axially on one end of the hub shell, and a drive cylinder, which constitutes the freewheel, is fixed onto the outer periphery of the tubular support by means of press-fitting.
Furthermore, the freewheel consists of a driven cylinder having transmission pawls on the outer periphery thereof; a driving cylinder which has at least one sprocket wheel on the outer periphery thereof and a ratchet on the inner periphery thereof; and a pair of ball bearings provided between the driven cylinder and the driving cylinder a unidirectional rotation transmission mechanism is formed by the ratchet and transmission pawls, so that the freewheel operates to transmit the driving rotation in one direction of the driving cylinder to the driven cylinder through the unidirectional rotation transmission mechanism and to allow the driven cylinder to freely rotate with respect to the rotation in the other direction of the driving cylinder. The power transmitted to the driven cylinder is transmitted through the hub shell, to which the driven cylinder is fixed, onto a bicycle wheel supported to the hub shell mainly by spokes.
In the above-described conventional construction where there is also provided the conventional feature that the driven cylinder is pressfitted to the tubular support at the hub shell to assemble the freewheel therewith, it is extremely difficult to remove or dismantle the freewheel from the tubular support in case of replacement, for example, of damaged transmission pawls at the freewheel. Furthermore, the repeated removal and application of the driven cylinder with respect to the tubular support will develop the problem of causing looseness between the driven cylinder and the tubular support, with the result that they are not ensurely rigidly fit with each other.
A construction was previously designed by the present inventor in order to overcome this problem as described in Japanese Utility Model Application No. Sho 56-165,563 filed on Nov. 5, 1981. The previous invention is described as follows: The axial length of the tubular support at the hub shell is made longer than that of the driven cylinder and the driven cylinder is loosely mounted on the tubular support. The tubular support is provided an outer end periphery thereof with an outer screw-thread portion and an inner end periphery thereof with a large number of splines. A lock ring having a rotation operation portion at an axial outside surface is screwed onto the outer screw threaded portion of the tubular support, so that the driven cylinder which is coupled to the tubular support by splines is readily mountable to and removable from the tubular support. However, with the above mentioned invention, since it is inevitable to form the rotation operation portion for the lock ring at the axial outside surface thereof as abovesaid as a result of the construction of a freewheel, it is necessary for the rotation operation of the lock ring to use a special tool that is applied to the rotation operation portion formed at the lock ring to rotate the same when mounting or removing the driven cylinder with respect to the tubular support. Additionally, there arises a possibility of damage to the rotation operation portion. Furtheremore, it is impossible to lessen the axial length of the driven cylinder of the freewheel assembly because the driven cylinder must hold the transmission pawls, and since balls are provided on the end portions of the hub shaft in order to rotatably support the hub shell, the length of the tubular support is subjected to a limitation. It is also impossible to make larger the length of the screw-threaded portion provided on the end periphery of the tubular support, resulting in the problem of being unable to obtain a sufficient fixing efficiency of the lock ring screwed onto the screw threaded portion of the tubular support.